1. Field
The present description relates to an ESD transistor and to an ESD transistor for high voltage applications that can shunt ESD current at a high level while reducing clamping voltage by forming an extended current path in the ESD transistor.
2. Description of Related Art
Electrostatic discharge (hereafter, referred to as “ESD”) is very important for reliability of most integrated circuits or core circuits. Circuit designers can protect a core circuit by implementing an ESD protection circuit connected with an I/O pad and connected to a ground GND, using an ESD transistor that is connected with the core circuit in parallel.
FIG. 1 is a block diagram illustrating an ESD protection circuit.
Referring to FIG. 1, an ESD protection circuit includes a floating-body transistor 101 (or clamp) that includes a body 102, a gate 103, the source 104, and the drain 105. The ESD protection circuit connects to an I/O pad 110 through the drain 105 of the floating-body transistor 101 and to a ground 120 through the source 104 of the floating-body transistor 101. The gate 103 of the floating-body transistor 101 is connected to the source 104, and a core circuit 130 is connected to the drain 105 and the source 104 in parallel with the floating-body transistor 101.
However, the ESD protection circuit with the illustrated configuration may exhibit difficulties in shunting high-level ESD currents while maintaining low clamping voltages. For example, in a transistor using high voltage over 20V, the doping concentration in the source 104 and the drain 105 should be low in order to maintain high break down voltage in the ESD protection circuit. However, during an event of electric discharge, the ability of the ESD protection circuit to protect the core circuit 130 decreases due to the high turn-on voltage induced in the operation of a GGNMOS and a bipolar junction transistor (BJT). Even in the event that the ESD protection circuit is turned on, strong snapback results due to a kirk effect in a high current bipolar operation mode.
In turn, the high turn-on voltage and the strong snapback may result in the generation of interface current and a change of BJT turn-on voltage due to a damage that may occur around a field insulating film (or a field oxide film) that exists between a drift doping region and a N+ doping region of the floating-body transistor 101.